topic Re: Intersecting a flood raster with a population grid in ArcGIS Spatial Analyst Questions

Intersecting a flood raster with a population grid

deleted-user-qIrrkfi_YpZh — Tue, 21 Aug 2018 17:50:48 GMT

I have two rasters: a flood inundation raster (depth grid) and a census grid. I would like to know how many people are affected at 0-1 feet, 1-3 feet, 3-6 feet, 6-9 feet, and more than 9 feet. I need to figure out how many are effected in each class (a count). What tool(s) do I need to use? Do I need to convert one (or both) rasters to a polygon? Thanks in advance!

Re: Intersecting a flood raster with a population grid

DanPatterson_Retired — Tue, 21 Aug 2018 18:10:17 GMT

Combine—Help | ArcGIS Desktop

will give you all the combinations. You have integer rasters and they are classified..

If your population isn't in classes, then

Zonal Statistics as Table—Help | ArcGIS Desktop

might do it

You should do the conversion to raster explicitly because you will need to establish the cell size, processing extent and set your snap raster (to the existing raster extent)

Re: Intersecting a flood raster with a population grid

XanderBakker — Tue, 21 Aug 2018 18:18:37 GMT

In addition to what Dan mentions, if your population is expressed as density you will need to convert the density to number of people using the area of overlap. If they are absolute values, use the fraction of overlap to get the correct number of people.

Re: Intersecting a flood raster with a population grid

deleted-user-qIrrkfi_YpZh — Tue, 21 Aug 2018 18:46:15 GMT

Wouldn't I need to convert my flood inundation raster to polygon so I had a "zone" to refer to?

My census grid is number of # people/cell

Re: Intersecting a flood raster with a population grid

DanPatterson_Retired — Tue, 21 Aug 2018 20:14:41 GMT

zonal statistics as table will convert a polygon back to a raster in any event... check the link I posted